Dual loop heat pump or refrigeration systems which utilize a linear motion free-piston expansion-compression device are known in the art. An example of such system is disclosed in U.S. Pat. No. 2,637,981 which also utilizes a single working fluid in each of the loops of the system. Such systems have a power loop which operates on a Rankine cycle and a refrigeration or heat pump loop which operates on a vapor compression cycle. One of the disadvantages with these prior art systems is that the operational efficiency thereof is poor because the linear momentum and temporary storage of kinetic energy in the free-piston assembly is not utilized to compress the working fluid in the refrigeration or heat pump loop, but rather is mechanically absorbed in the compression device. This has resulted in such prior art systems being unfeasible economically and in some cases creating a system that was virtually impossible to reduce to practice. These systems have also required a relatively high operating temperature and pressure for the power loop working fluid thereby limiting the operating range of such systems. Also, a highly irreversible energy wasting throttling process must be used in these prior art systems.